A diamond tool according to the present invention is applied to building stone tools such as a saw, a core drill, a cutter, a saw blade, a wire saw, a polishing cup, a profiler and an end mill, and also to precision tools such as a straight wheel, an ID wheel, a rotary dresser and an edge grinding wheel, or the like.
In general, the diamond tool is comprised of a shank and a diamond grinding stone portion (“diamond-impregnated section”) attached to the shank and for cutting and grinding a workpiece. Here, the diamond-impregnated section is constructed of plural diamond particles and a metallic bonding material. Diamond generally refers to a synthetic and natural diamond, cubic boron nitride (cBN), and additionally a super abrasive such as silicone carbide and alumina, and a mixture of at least two of the aforementioned materials. Further, the shank as used herein is commonly formed of a metallic material such as stainless steel and carbon steel.
As a method of bonding the abrasive or diamond-impregnated section to a shank, it is well known a sintered-tip welding method (hereinafter, referred to as a “sintering method”), an electroplating method, a brazing method, or the like. In the sintering method, generally, a metallic bonding material and abrasives are mixed, press-compacted, and sintered to form a cutting tip, and then the sintered cutting tip is bonded to a shank through a brazing or laser welding. In the electroplating method, abrasives are attached to a shank through a wet electroplating process using a bonding material such as nickel. In the brazing method, a liquid paste of a metallic bonding material and a binder is coated on the shank, abrasives are dispersed therein, and the dispersed abrasives are bonded to the shank at elevated temperature. FIG. 1 is a sectional view of abrasives 130 bonded to a shank 110 via a bonding material 120 respectively through a sintering method (FIG. 1 (a)), an electroplating method (FIG. 1 (b)), and a brazing method (FIG. 1 (c)).
FIG. 2 is a front view of a saw blade where abrasives 130 are bonded to a shank 110 through a sintering method. FIG. 3 is a sectional view taken along the line II-II in FIG. 2. As described above, according to the sintering method, the metallic bonding material 120 and abrasives 130 are mixed, press-compacted, and sintered, and thus the plural abrasives 130 are non-uniformly dispersed in the metallic bonding material 120, as shown in FIG. 3. This cutting tip is bonded to the shank 110 through a weldment 115 formed by a laser welding, a resistance welding, or a silver brazing.
FIG. 4 is a front view of a saw blade where abrasives 130 are bonded to a shank 110 through a brazing method or an electroplating method. FIG. 5 is a sectional view taken along the line III-III in FIG. 4. As described above, in the brazing or electroplating method, the abrasives are directly attached to the shank 110, and thus the abrasives 130 is bonded to the surface of the shank 110 in a mono-layer.
Above about 80% of diamond tools are manufactured by the sintering method. In the diamond tools formed by the sintering method, abrasives are distributed in a multi-layer and non-uniform fashion, and the sintering method cannot he readily applied to a very complicated shank. In contrast, the electroplating and brazing method can form a single non-uniform abrasive layer or a uniform abrasive layer, and thus suitable to manufacture a diamond tool having a complicated structure. In addition, the sintering and electroplating methods do not associate a chemical reaction between diamond particles and the metallic bonding material to thereby involve a mechanical bonding having a relatively weak retention force. In the brazing method, a strong chemical bonding is occurred in the interface between the abrasives and the metallic bonding material, and thus the abrasives are rarely released during the use of tools. In addition, it does not necessitate a time and cost consuming dressing process, and can be used in a bi-directional cutting and grinding process. Accordingly, diamond tools manufactured through a brazing method have a good cutting performance, as compared with ones manufactured by a sintering or electroplating method, and in particular, provide appropriate characteristics to a dry process or DIY (Do-It-Yourself) products. Furthermore, the brazing method can maximize exposure of the abrasives, control the abrasive spacing precisely, and form a chip pocket to thereby enable a smooth mobility of slurry and grinding agent. Moreover, in a case where Ni—Cr alloy is used, the presence of Cr leads to a good corrosion resistance.
As described above, the brazing method has various merits. FIG. 6 explains a process for bonding abrasives to a shank according to a brazing method. As shown in FIG. 6, a bonding material 120 containing a brazing powder (metal powder) of paste form is coated on a shank 110 (FIG. 6 (a)), and then, plural abrasives 130 are dispersed in the coated paste (FIG. 6 (b)). Here, the paste bonding material 120, which is used to bond the abrasives 130 to the shank 110, commonly contains metal powder and a binder providing fluidity to the metal power. In addition, a drying process may be provided between the bonding material coating and the abrasive dispersion. The coated bonding material 120 and the abrasives dispersed therein are dried at a certain temperature (FIG. 6 (c)). Thereafter, the resultant product is held in a vacuum furnace or a reduction/inert gas atmosphere furnace at a certain elevated temperature, where the metal power in the bonding material can flow in a liquid phase and react chemically, such that the brazing metallic bonding material is melted and solidified in the shank 110 and the abrasives 110 (FIG. 6 (d)). At this time, the holding temperature depends on the type of the commercialized pastes, for example, about 600˜1300° C. The heat source for the vacuum furnace mostly employs a high-frequency heating, a direct heating, or an indirect heating. In case of using the gas atmospheric furnace, a continuous type gas furnace using a conveyor can be utilized to thereby enhance the production efficiency, as compared with a vacuum furnace, which is mostly a batch type furnace.
As described above, in the sintering method, metal powder as a bonding material and abrasives are mixed, press-compacted to a certain desired shape, and sintered, and therefore the abrasives are formed in multi layers. Thus, although the abrasives are released during use of the tool, a lower abrasive layer is continually exposed and participates in the cutting and grinding work, thereby extending the service life of the tool. In case of the brazing method, however, the abrasive 130 is attached to the shank 110 in a single layer, and thus, the release of abrasives through a long time service is inevitable although the abrasives are bonded to the shank and the boding material by a strong chemical bonding. Therefore, the service life thereof is disadvantageously shortened, as compared with the case of sintering method.
As an alternate method of forming a multi-layer fusion-bonded layer of abrasive, for example, a lower abrasive layer is formed according to the process of FIG. 6, which is repeated to thereby form an upper abrasive layer. In this case, during a second heat treatment for fusion bonding the upper abrasive layer, when the metal powder of a bonding material constituting the upper abrasive layer is melted, the metal bonding the abrasives and the shank in the lower abrasive layer is melted again. In this way, the metal powder in both the lower and upper abrasive layers is melted to thereby form a thick molten metal layer, which can easily flow under the gravity force. Therefore, the abrasives uniformly dispersed in the lower and upper abrasive layer are scattered in a random fashion and deviated with its thickness, so that the cutting or grinding ability may be deteriorated. In addition, the multiple abrasive layers, which are formed through a multi-layered melting by the repetition of process, cannot have a uniform mechanical property between layers and may causes a stratification when in use, thereby significantly deteriorating the cutting and grinding performance thereof.